Valve devices for pressurised gas cylinders are known in the prior art. These valves generally comprise a control handwheel or button rotated by the user to control a flap closing the gas inlet. The flap is generally integral with the control handwheel via a gate valve stem. The flap is therefore very often rotated at the same time as the handwheel until it closes the gas inlet. The flaps generally comprise on their closing end a packing which is applied against the gas inlet seat. When the user screws the handwheel excessively in order to fully close the gate valve, the inlet duct seat tends to sink into the packing. When the user then wishes to open the gate valve, it may prove difficult to turn the control handwheel, given the fact that it sunk into the flap packing and therefore that multifarious friction exists between the flap and the duct seat.
An object of the invention is to provide a new and improved closing device for use in a gas valve device for overcoming the drawbacks of the prior art.